Mass-balance modeling of mineral weathering rates and CO2 consumption in the forested, metabasaltic Hauver Branch watershed, Catoctin Mountain, Maryland, USA
Version of Record online: 10 JAN 2013
Copyright © 2013 John Wiley & Sons, Ltd.
Earth Surface Processes and Landforms
Volume 38, Issue 8, pages 859–875, 30 June 2013
How to Cite
Price, J. R., Rice, K. C. and Szymanski, D. W. (2013), Mass-balance modeling of mineral weathering rates and CO2 consumption in the forested, metabasaltic Hauver Branch watershed, Catoctin Mountain, Maryland, USA. Earth Surf. Process. Landforms, 38: 859–875. doi: 10.1002/esp.3373
- Issue online: 14 JUN 2013
- Version of Record online: 10 JAN 2013
- Accepted manuscript online: 29 NOV 2012 08:48PM EST
- Manuscript Accepted: 26 NOV 2012
- Manuscript Revised: 19 NOV 2012
- Manuscript Received: 14 NOV 2011
- metabasalt chemical weathering;
- biomass nutrient uptake stoichiometry;
- watershed mass balance;
- CO2 consumption;
- saprolitization rates
Mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested, metabasaltic Hauver Branch watershed in north-central Maryland, USA. Previous studies of Hauver Branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering, including biomass. More equations in the mass-balance matrix were added using existing mineralogic information. The stoichiometry of a deciduous biomass term was determined using multi-year weekly to biweekly stream-water chemistry for a nearby watershed, which drains relatively unreactive quartzite bedrock.
At Hauver Branch, calcite hosts ~38 mol% of the calcium ion (Ca2+) contained in weathering minerals, but its weathering provides ~90% of the stream water Ca2+. This occurs in a landscape with a regolith residence time of more than several Ka (kiloannum). Previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream Ca2+/Na+ ratios. The relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone.
Of the carbon dioxide (CO2) consumed by mineral weathering, calcite is responsible for approximately 27%, with the silicate weathering consumption rate far exceeding that of the global average. The chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles, and therefore, climate, on geological timescales. Based on carbon-balance calculations, atmospheric-derived sulfuric acid is responsible for approximately 22% of the mineral weathering occurring in the watershed. Our results suggest that rising air temperatures, driven by global warming and resulting in higher precipitation, will cause the rate of chemical weathering in the Hauver Branch watershed to increase until a threshold temperature is reached. Beyond the threshold temperature, increased recharge would produce a shallower groundwater table and reduced chemical weathering rates. Copyright © 2013 John Wiley & Sons, Ltd.